705140 - [ASC BUG] ASC computes wrong type for result of the "as" operator, errors out in strict mode

Status: RESOLVED FIXED

(Tamarin Graveyard :: Tools, defect, P2)

Description

[Virgil Palanciuc]

The new ASC gives compilation errors on code like the following:
  var stroke:GraphicsStroke = istroke as GraphicsStroke;		

since the "as" operator may return "null", I'm guessing it interprets the type of the expression as "Object" and punts on assignment to GraphicsStroke; (example from avmglue/Graphics.as). 
A possibly special (but similar) case is when a Number is converted to "uint" via "as" - e.g.
var a:Number = value;
var b:uint = a as uint;
example: avmglue/System.as, "return totalMemoryNumber as uint" (though in this particular case the usage of 'as' may actually be a bug, IMO).

Comment 1

[Lars T Hansen]

Complete test case (file asc.as) that requires only builtin.abc:

------ 8>< ------------------------
function f(y)
{
  var x:Date = y as Date;
  return x;
}
------ 8>< ------------------------

Error:

[Compiler] Error #1118: Implicit coercion of a value with static type Object
   to a possibly unrelated type Date.
   asc.as, Ln 3, Col 15: 
   	var x:Date = y as Date;
   ..............^

Comment 2

[Lars T Hansen]

Attachment: Tentative fix

This fixes the problem and probably does not throw away any useful type information.  However, it is possible that the correct fix is really elsewhere, for example, in the type matching for assignment or initialization.

We need more test cases to determine if argument passing and assignment are afflicted in the same way initialization is.

Comment 3

[Lars T Hansen]

Further testing shows that argument passing and assignment are also affected.  Concluding that the proposed fix is good enough.